I am building a 66 289 engine for a Cobra kit car and was wondering if anyone has used one of these. My question is in regards to "fit". I plan on using an Edelbrock RPM airgap manifold and was concerned about getting full advance/retard by turning the distributor to its limits to set the timing. I know this is larger in diameter than a Mallory unit I had before (in a similar 289 but I was using an F4B intake at that time) and with the Mallory, I could not get full movement with a smaller cap. Davis wants a 20% restock fee and I dont want to buy if it wont work. I like this as it is a single wire setup to keep the engine bay clean and they will set advance curve (mechanical) to my vehicle by weight, type trans. cam specs, etc. Anyone using one and pros and cons? Thanks in advance. Brian